4N[sic]Hazem Ali

ELECTROCUTIONHazem Ali

SOURCE Low-Voltage Lines (Domestic): varies from country to country

USA: 110 – 120 V, 60 Hz “cycles per second” (AC) Egypt, Europe: 220 – 240 V, 50 Hz (AC)

High-Voltage Lines 1ry distribution power lines: up to 20,000 V High tension power lines (towers): up to 100,000 V

Industrial: Very high voltage: up to 400,000 V

Natural: Lightning

SOURCE Direct current (DC):

Flows constantly in the same direction Less commonly used (some industries)

Alternating current (AC): reverses its direction at regular intervals Commonly used in household devices

Why AC is more dangerous than DC? More commonly used (more accidents) More risk for muscle spasm “hold-on” and cardiac arrhythmia The danger to the body exists when the rate lies between 40 and 150 Hz

“cycles per second” An increase/decrease in rate above/below this range decreases the danger. E.g. at 1720 cps the heart is 20 times less likely to fibrillate than at 150 cps

PHYSICS

(I) amount of current flow (V) electromotive force (R) resistance to the conduction of electricity

PHYSICSAmperage (Current): The actual amount of electricity flow (number of electrons per unit time)

Current is the most important factor in electrocution: A current of high voltage with low amperage can be less dangerous

than one with moderate voltage but high amperage

Factors affecting amperage: Voltage (direct relation) Resistance of the tissue (inverse relation) Time for which the current is flowing (affects degree of tissue damage)

PHYSICSAmperage (Current): Current of 1 mA tingling sensations Current of 5 mA muscle tremors Current of 8-20 mA muscular spasm “hold-on” Current around 40 mA loss of consciousness Current of 75-100 mA ventricular fibrillation Current above 1 ,000 mA (1 A) cardiac arrest

In this case, the heart should start beating normally after the circuit is broken (provided no irreversible damages occurred to the heart)

Current above 4 A is used to arrests ventricular fibrillation “defibrillator”

PHYSICSVoltage (Tension): The “Force” required to produce 1 ampere of intensity when passed through a conductor having the resistance of 1 ohm

Most fatalities follow shocks from currents of 220–250 V, which is the usual range of household supply Low voltage (below 50 V) usually non-fatal

Voltage below 500 V muscular spasm and “hold-on” effect Voltage above 500 V severe muscular contractions that throw the victim away

PHYSICSDuration of Contact: The longer the contact, the greater will be the damage

Low-amperage current needs longer time (i.e. minutes) to be lethal By respiratory muscle spasm

High-amperage current needs shorter time (i.e. seconds) to be lethal By ventricular fibrillation

PHYSICSResistance of tissues: The major barrier to the electric current is the skin

The blood vessels in the dermis serves as a favorable medium for the passage of current filled with electrolyte rich fluid

Factors affecting resistance of skin: Thickness of the keratin-covered epidermis:

palms and soles are more resistant than thin skin Dryness of skin:

dry hands/feet can offer up to 1 million ohms of resistance Wet skin (from sweating or external moisture) offers 1000 ohms or less

Area of contact

PHYSICSArea of Contact of the Body: The smaller area of contact between the skin and the electric supply will exert more resistance than the larger area Tip of dry finger > palm of wet hand > wet body in a bath

Passage of a current through a localized area of contact also generate sufficient heat to burn the skin This is why electrocution in a bathtub may occur without any external mark

The current passage through vital organs (e.g. heart, brain) is more dangerous

CAUSE OF DEATH The current tends to run from the point of contact to the point of grounding,

following the shortest path, not necessarily the path of least resistance Common entry site: hand Common exit site: foot, other hand

1ry causes of death: Ventricular fibrillation (most common) Spasm of the respiratory muscles Paralysis of the brainstem centers

2ry causes of death: Head/Body injuries from falling from height Complications of severe burns (high-voltage lines)

CAUSE OF DEATH Ventricular fibrillation:

When the current passes through the thorax, from hand to hand or from hand to leg routes

Cardiac arrest Pallor (No cyanosis)

Spasm of the respiratory muscles: When the current passing through the thorax may lead to tetanic contraction of the

muscles of respiration Respiratory arrest Cyanosis (congestive hypoxia)

Paralysis of the brainstem centers: when the current passes through the head (rarely when unprotected head touch the

source) The current can damage brainstem and leads to paralysis of cardiac and/or

respiratory centers

JUST BEFORE DEATH It is very common for the individual receiving a fatal electric shock to not lose consciousness immediately, but to yell out or state that he just “burned” himself prior to collapse.

This is because the brain has approximately 10–15 sec of oxygen reserve, irrespective of the heart. Thus, an individual can remain conscious for 10–15 s after cessation of the

heart as a pumping organ

MANNER OF DEATH Most common accidental

Rarely suicide

Extremely rare homicide

Some states in America judicial “electric chair”

SCENE INVESTIGATION Scene investigation is the key to the diagnosis of electrocution

First step, be sure that electricity is turned off

Victim status: Clothed/naked Simple cloths/protective gloves or shoes Dry/wet skin Points of contact with the source/ground.

Clothes of the victim should also be described and preserved properly E.g. burn defects

SCENE INVESTIGATION Pay attention to all electrical devices, tools, machines (especially older or poorly maintained ones) Look for circuit defects Look for retained skin/hair of victim

Pay attention in all work-related deaths Electrocution is a usual suspect

Pay attention in all watery environment-related deaths (bathtubs, swimming pools) Even if no suspicious lesions grossly

AUTOPSY In cases of cardiac arrest:

Pallor (no cyanosis)

In case of respiratory arrest: Cyanosis Visceral congestion Petechial hemorrhages

In case of violent muscle contraction: Accelerated onset of rigor mortis Long bone fractures If the individuals are grasping something, they will continue to do so.

AUTOPSYEntry marks:(1) Collapsed blisters:Mechanism:

When firm contact to conductor Generated heat splits the skin layers blister On cooling collapse

Gross: Usually hands, fingers Small (few mm – 1 or 2 cm) Firm, Round –oval areas

If the contact is with the long axis of the wire linear groove Zones:

Central depression ‘crater’ Surrounded by raised edges of blanched skin

Due to arteriolar spasm by effect of electricity Outermost intact skin may be mildly hyperemic

AUTOPSYEntry marks:(2) Spark nodule:Mechanism:

When loose contact to conductor the current “spark” jumps the gap between the source and the skin

melting of keratin On cooling nodule of condensed keratin

Gross: Usually hands, fingers Small (few mm – 1 or 2 cm) Hard, brownish nodule Surrounded by areola of blanched skin (due to arteriolar spasm)

AUTOPSY

contact blister and adjacent spark burn

In many electrical burns these two types are combined as a result of:• Movement of the hand or body against the conductor• Irregularity of the shape of the conductor.

AUTOPSY The strong flexion of rigor mortis may bring the fingers down to the palms and obscure electrical marks

So it is essential in all autopsies (when electrocution is a possibility) to examine the flexor surface of the fingers by forcible breaking of the rigor and even cut flexor tendons at the wrist to release the rigor clenching of the fingers

AUTOPSYExit Marks: Usually feet

Variable in appearance but usually have some of the features of entry marks

More tissue disruption, even skin laceration

Burns and perforations of the clothing or shoes may be seen

AUTOPSYSo, is electric mark helpful and diagnostic? - NO Can varies in size and shape

depending on many factors especially area of contact

Can be absent If area of contact is large (as in deaths occurring in the bathtub) If area of contact in hidden place (as in deaths of children holding wire in their

mouths)

Can't be differentiated from thermal burn Can give similar gross and microscopic features Scanning E/M can be helpful in these cases

Can’t differentiate ante-mortem from post-mortem injuries Gives the same picture (unless outside zone hyperemia)

AUTOPSYHigh-voltage current Exposure:

Direct contact Current “arcing” over several centimeters without real contact

Effects: Multiple individual and confluent burns and charring

High-voltage currents can produce extremely high temperature (up to 4000 C) Bone fractures Even loss of extremities or organ rupture can be seen

“Crocodile skin” effect: Multiple, discrete, punched-out burns Dancing of current sparks over the body

AUTOPSYMultiple individual and confluent burn areas‘Crocodile skin’

HISTOPATHOLOGYSkin: Epidermis:

Coagulative necrosis of epidermis and corium

Separated epidermal layers from each other or from the corium “blisters”

Show variable sized micro-spaces in the corium and epidermis “honeycomb appearance”

Epidermis cells are flattened, elongated, with their nuclei become horizontally stretched, streamed (especially basal cells)

Blackish carbonization of the epidermis “electrical metallization”

HISTOPATHOLOGYSkin: Dermis:

Homogenization (denaturation) Cells of the skin appendages may show similar damage as epidermis cells

Subcutaneous fat: Fat cells in severe cases may appear to be “cooked” and display a homogenous, golden color

ALL the previous features can be shown in thermal injuries (non-specific)

Electron microscope and Chemical analysis can help solving these problems as it can detect metallic deposits in electrical injuries

HISTOPATHOLOGY Bubbly coagulation necrosis of the

epidermis

Blister formation

HISTOPATHOLOGY

Coagulative necrosis of the epidermis, with a glassy purple/pink appearance (asterisk) Large vacuoles (arrowhead) The nuclei become wavy and stretched out (arrow)

HISTOPATHOLOGY

Separation of the epidermis from the dermis (↑) Microblisters, best seen in the thick stratum corneum (→)

Represent channels made by escaping steam. Dermal collagen is denatured, producing homogenous, pronounced hematoxylin staining (↓)

Compare it with the dermal collagen on the right side of the photo.

HISTOPATHOLOGY Microblisters at epidermis (arrow) Streaming of nuclei

HISTOPATHOLOGY

Microblisters in the stratum corneum Charring of the surface (arrow).

Metal fragments from the point of skin contact may be seen

HISTOPATHOLOGYHeart: Damage to Conductive system: (fatal arrhythmia)

No Pathology (common) Waviness and fragmentation

Damage to Vascular system: Rupture Hemorrhage Spasm Acute infarction Wall damage Micro-thrombi

Damage to Myocardium: Contraction bands Necrosis (+/- cellular reaction depending on survival time) Hemorrhage

Again, ALL these features are non-specific

HISTOPATHOLOGYSkeletal Muscle:

Similar to cardiac muscle damage (hemorrhage, necrosis)Lung:

Congestion, petechial hemorrhage Bone marrow emboli (in cases of long bone fractures)

Kidney: Myoglobinuria from rhabdomyolysis

Brain: Congestion, petechial hemorrhage Axonal fragmentations Shrinkage of neural tissue with widening of perivascular spaces

Again, ALL these features are non-specific

LIGHTNINGHazem Ali

PHYSICS Benjamin Franklin (1706–1790) discovered that lightning flashes were electrical discharges and not gaseous explosions

In lightning, the discharge may be: From cloud to cloud From cloud to the earth (through tallest object in contact with earth)

95% of lightning discharges are negative (only 5% are positive)

Lightning chooses the path of least resistance (not the shortest)

PHYSICS The lightning characterized by:

Direct current with 20,000 amperes And a million volts Over an average period of 30 microseconds

Lightning hits the victim by: Direct hit (strike) Indirect hit:

Side-flash: lightning hits intermediate non-metal object (e.g. tree) arc to the victim (nearby one)

Conduction: lightning hits intermediate metal object (e.g. water pipe) flows through it to the grounded victim (bathtub)

CAUSE OF DEATH Damaging mechanisms:

Direct effect (strike itself) Burns (due to generation of huge amount of heat) Blast effect (due to rapidly expanding air by heat) Compression effect (due to return waves of air)

Causes of death: Brain injury: paralysis of respiratory and/or cardiac centers Heart injury: arrest Electro-thermal injuries: burns and its complications Blast injuries: lacerations, fractures, and organs rupture

SCENE INVESTIGATION Tearing, bursting or ripping of clothing or shoes

Sometimes gives a false impression of criminal assault / rape

Damage to the ground, houses, trees or animals

Metallic objects in the area may get melted, fused Iron objects become magnetized

History of thunderstorm could help solving the difficult cases

AUTOPSYSinging of the body hair

Surface “Contact” burns:• Due to molten or heated up metallic objects worn or carried by the victim• Some melted metal may be implanted into the skin

Linear burns: Due to current passage through area of the skin offers lesser resistance

i.e. moist creases and folds of the skin

Arborescent “Fern-like” burns: Unknown mechanism Seen in 1/3 of cases• Patterned “fern-like” area of transient erythema over shoulders and flanks• Starts after 1 hours and Fades within 24 hours if the victim survives

AUTOPSY

Arborescent or filigree burns

AUTOPSYBlast effect:

Severe lacerations, fractures, organs rupture

Ruptured tympanic membranes (with blood flow from external ear) Can be misinterpreted as head trauma

THANK YOUHazem Ali